1. Field of the Invention
The present invention relates to a diffractive display device, and a finder device and a camera.
2. Discussion of the Background
There have conventionally been known intrafinder display devices making a display within a finder scope of a camera by superimposing a variety of information such as a focus detection area on an object image, a so-called superimposed display. Among these intrafinder display devices, for example as shown in later-described Patent Document 1, a diffractive display device capable of displaying a liquid crystal hologram has been developed.
In the diffractive display device shown in this Patent Document 1, an optical material layer is sealed within a transparent substrate, and this optical material layer forms a refractive index grating having a periodical layer configuration made up of refractive index isotropic regions and refractive index anisotropic regions within a polymer distributed liquid crystal. When illumination light is entered from the side surface of the optical material layer between the substrates, the light is diffracted by the refractive index grating of the optical material layer and emitted from the surface of the transparent substrate in a pentaprism direction, and letters and graphics formed by the diffraction light can be observed as intrafinder displays.
Typical examples of the conventional intrafinder displays include a mark display of a focus detection area or the like. Recently, there are cases where mark displays of a plurality of focus detection areas are desired to be made.
However, in the diffractive display device, for example as shown in Japanese Unexamined Patent Publication No 2004-191415, when a plurality of mark displays are intended to be made within the finder scope, luminance of diffraction light decreases depending upon positions of the mark displays, which might cause occurrence of non-uniformity of luminance within the surface.
Further, an attempt has also been made recently to increase a cell size of the diffractive display device, and when the cell size is increased, a problem of attenuation of light after entering into the optical material layer occurs, and especially luminance of a mark display located on the opposite side to the light entering surface tends to decrease.